The present invention relates to polymeric compositions and to intraocular lenses made from such compositions. More particularly, the invention relates to polymeric compositions which have high refractive indexes and to intraocular lenses, preferably deformable intraocular lenses, made therefrom.
Intraocular lenses (IOLs) have been known for a long time, since shortly after the end of World War II. Such a lens is surgically implanted into a mammalian eye, e.g., human eye, to replace a damaged or diseased natural lens of the eye and restore the patient's vision.
Although IOLs are made from "hard" or "rigid" polymeric or glass optical materials, such as polymethylmethacrylate (which has a refractive index of 1.48), soft resilient polymeric materials, such as silicones, have been increasingly used, for the reasons discussed below, in ophthalmic applications.
Since soft IOLs are deformable, for example, foldable or rollable, for implantation, a smaller incision can be surgically cut in the eye than for the implantation of "hard" IOLs of the same optical power. The smaller the incision, the less trauma the patient's eye experiences and the faster post-operative healing occurs. An incision of about 3 mm is ideal since this size incision is presently required to remove the natural lens after it has been broken up, for example, emulsified in a conventional phacoemulsification procedure. In contrast the typical IOL optic has a diameter of about 6 mm.
The size and mechanical characteristics of the deformable IOLs play an important role. As is well understood by those skilled in the art, for successful implantation, the deformable IOL must have sufficient structural integrity, elasticity and elongation and be small enough in size to permit deforming for insertion through a small incision. After insertion, the lens must, of course, regain its original shape and have sufficient structural integrity to retain such shape under normal use conditions.
In general, the thinner the deformable IOL the smaller the incision in the eye that is required. On the other hand, in order to function optically as an IOL, the lens must have sufficient optical refractory power. Also, the higher the optical refractive index of the material making up the IOL, the thinner the IOL can be and still obtain the same optical refractory power.
IOLs made of silicone polymeric materials conventionally have refractive indexes which are no greater than about 1.46. Consequently, their center thicknesses are substantially greater than those of IOLs composed of materials having higher refractive indexes. Deformable IOLs made of acrylic materials can be too rigid for use at room temperature, which rigidity can result in cracking if the IOL is folded quickly; can be near silicone polymeric materials in refractive index; or can be quite tacky in nature, which tackiness inhibits deforming to a sufficiently small size for insertion through a very small incision and may cause handling problems.
Gupta U.S. Pat. No. 4,834,750 discloses IOLs with optics made of copolymers of methacrylate esters which form homopolymers that are relatively hard at room temperature and acrylate esters which form homopolymers that are relatively soft at room temperature. Such copolymers are crosslinked with a diacrylate ester to produce an acrylic material having a tack-free surface and a glass transition temperature in the range of -30.degree. to 25.degree. C. This patent discloses that such optics can be deformed for insertion into the eye. However, this patent is silent on the refractive index of IOL optics and is, thus, unconcerned with forming deformable IOLs with high refractive indexes. For example, none of the specific monomers disclosed in this patent provide homopolymers which have a refractive index of at least about 1.50.
It would be advantageous to provide an IOL material of construction which has good optical properties, including optical clarity and high refractive index, and has sufficient characteristics and properties to provide an IOL which is effectively deformable for insertion through a small incision.